This invention relates to a molding process for producing hollow articles, particularly full length Foley catheters. In the past, hollow articles have been produced by a variety of dipping, molding and extrusion apparatus and processes. However, each of these prior art processes and apparatus have suffered from disadvantages that are substantially overcome by the present apparatus and process.
In the dipping processes known in the prior art, a wire is dipped into a liquified material to be formed into the hollow article. With each dip of the wire more product from the bath adheres to the coated wire until eventually the desired amount of material is built up onto the wire. Then the material coated on the wire is sufficiently hardened so as to permit the hollow article surrounding the wire to be peeled or stripped therefrom. One disadvantage of the dipping process is the large number of dips and great amount of time sometimes required to build up the desired amount of material on the wire. Additionally, when the hollow article to be manufactured requires small diameter wires, many materials are too viscous in a liquified state for the wire to be dipped therein without bending of the wire.
As with the above described prior art dipping processes, other prior art processes also have disadvantages. For instance, extrusion processes are not advantageously employed to obtain products with a closed end. Further, while many molding processes may be employed to obtain products with closed ends, these processes are generally not advantageously employed when the article is relatively long and slender. The reason for this is that the portion of the mold defining the hollow portion of the final product is often unstable and bends at the high pressures employed in the molding process.
The above noted deficiencies in prior art processes and apparatus are substantially overcome by the process and apparatus disclosed in U.S. Pat. application Ser. No. 580,881, filed May 27, 1975. The apparatus of the above-noted application comprises a mold cavity with a first wire longitudinally disposed therein. A second wire may be spaced distally from the distal end of the first wire in longitudinal alignment therewith. Upon injection of molding material into the mold, said material flows longitudinally toward the distal end of the mold cavity pushing the follower ahead of it. When the follower reaches the distal end of the first wire, it continues to move distally in the mold onto the second wire thereby bridging the gap between the first wire and the second wire. Eventually, the follower disengages entirely from the first wire to provide a hollow article with a solid tip. If a hollow article without a solid tip is desired, only one wire is used and the follower does not disengage from the wire.
The process described in the above-noted application has two disadvantages. First, it is difficult to produce long articles with relatively small hollow portions according to the process and apparatus disclosed because the small wire required is distorted by the high pressures required. For example, full length Foley catheters can not be produced by the process and apparatus disclosed in U.S. application Ser. No. 580,881 because the small inflation lumen wire is distorted by the high process pressures required to such an extent that the wire touches the mold wall to provide a useless inflation lumen with a hole in it. Second, when a hollow article with a solid tip is produced according to the process and apparatus of the above-noted application, the follower is transferred from a first wire to a second wire. However, the first wire may be twisted with respect to the second wire by the high pressures required, thereby preventing the smooth transfer of the follower from the first wire to the second wire. As described in U.S. application Ser. No. 580,881, the seriousness of this problem may be diminished by using specially designed followers and second wires in which the cross sectional area defined by the inside wall of the distal end of the follower is larger than the cross sectional area defined by the proximal end of the second wire. However, the specially designed follower and second wire of the above-noted application may not always accomplish their intended function, and at any rate, an apparatus and process that do not require a specially designed follower and second wire would be most desirable.
The process of the present invention may be used to produce hollow articles from a wide variety of materials, including materials which are too viscous in a liquid state to be used to produce hollow articles by prior art dipping processes. Additionally, the process and apparatus of the present invention may be employed to produce hollow products with one of the ends closed by a solid tip. Further, the process and apparatus of the present invention may be used to produce long articles with relatively small, long hollow portions, such as Foley catheters. Finally, the process of the present invention may be used to produce hollow articles with a solid tip without requiring the use of a specially designed follower and second wire.